This Nikon Travelite 10 x 25mm multicoated high power center focus porro prism binocular has aspherical elements in its eyepieces for low distortion, plus costly BaK-4 porro prisms for more performance than you might expect from its low price. Its lightweight black polycarbonate body is lightly rubber armored. Finger grooves are molded into the body for a secure grip. There are no sharp corners to snag clothing as the binocular slips into pocket, purse, or auto glove compartment.

This compact Nikon porro prism has soft rolldown rubber eyecups and a soft vinyl case that attaches to your belt for no-hands carrying. The diopter adjustment on the right eyepiece is a click-stop design that won’t accidentally get out of adjustment when you least want it to. The Travelite is a handy bino for nature walks, traveling, sports, the theatre, etc. – anywhere high power, compact size, and light weight are more important than very bright images in low light.

The 10 x 25mm Nikon Travelite is powerful enough to show you details in distant aeries and shore bird rookeries, yet will focus down to only 9.8’ for exquisite close-ups of backyard feeders as well – in fact, any birding or nature study situation where high power is essential, but very bright images and a high price are not. The 10 x 25mm shows hand tremors more easily than a lower power bino, so be sure its high power fits your needs before choosing it.

The optical design of a binocular or spotting scope. A binocular can be
either a porro prism (whose objective lenses are off-set and spaced
further apart than the eyepieces) or a roof prism (whose objective
lenses are in line with the eyepieces). A spotting scope can be either a
porro prism or roof prism refractor or a catadioptric (a combination of
lenses, mirrors, and prisms).

The circular image or beam of light formed by the eyepiece of a
telescope. To take full advantage of a scope's light-gathering capacity,
the diameter of an eyepiece exit pupil should be no larger than the 7mm
diameter of your eye's dark-adapted pupil, so that all of the light
collected by the telescope enters your eye. (The eyepiece exit pupil
diameter is found by dividing the eyepiece focal length by the telescope
focal ratio.) Your eye's ability to dilate declines with increasing age
(to a dark-adapted pupil of about 5mm by age 50 or so). For those in
this age group, eyepieces with exit pupils larger than their eyes can
dilate to simply waste their telescope's light-gathering capacity, as
some of the scope's light will fall on their iris instead of entering
their eye.

A number used to compare the brightness of binoculars or spotting scopes
of similar magnification. The relative brightness is determined by
squaring the diameter of the exit pupil. The larger the relative
brightness number, the brighter the image.

A number used to compare the effectiveness of binoculars or spotting
scopes used in low light. The twilight factor is found by multiplying
the size of the objective lens (in mm) by the magnification and then
finding the square root of that result. The larger the twilight factor,
the more detail you can see in low light. A twilight factor of 17 or
better if usually required for reasonable low light use.

Eye relief is the distance from the last surface of the eye lens of an
eyepiece to the plane behind the eyepiece where all the light rays of
the exit pupil come to a focus and the circular image is formed,
sometimes called the “Ramsden Disk.” This is where your eye should be
positioned to see the full field of view of the eyepiece. If you must
wear glasses because of astigmatism, you’ll usually need at least 15mm
of eye relief or longer if you want to see the full field of view with
your glasses on.

A note on our eye relief figures: Quite
often, our eye relief figures will differ from those of the
manufacturer. This is because we measure the “usable” eye relief, while
the manufacturers specify their usually-longer (but technically correct)
“designed” eye relief.

The eye lens of the eyepiece is normally
recessed below the rubber eyeguard or rubber rim of the eyepiece to keep
the lens from being scratched during use. An eyepiece might have a
“designed” eye relief of 15mm (and the eye relief will truly measure
15mm from the eye lens to where the image forms). However, if the eye
lens is recessed 3mm below the eye guard, the Ramsden Disk forms only
12mm above the eyepiece body (the 15mm “designed” eye relief, less the
3mm of eye relief made unusable by having the eye lens recessed into the
body of the eyepiece). This “usable” eye relief of 12mm (measured from
the rolled-down eyeguard – the closest point you can get your eye to the
eye lens – to where the image forms) is the eye relief figure we would
measure and list in this website.

Why is it important to list the “usable” eye relief? For
those people who don’t wear eyeglasses while observing, a few mm
difference between the eye relief they expect from the manufacturer’s
literature and the shorter eye relief they actually get in real life
doesn’t mean a lot. They can simply move a little closer to the eyepiece
to see the full field, and never realize that the eye relief is a
little shorter than they expected. However, some people must wear
eyeglasses while observing, because of severe astigmatism. These
observers can’t move closer to the eyepiece if the eye relief is shorter
than expected because their glasses get in the way. For these people,
the real life “usable” eye relief is more important than the technically
correct but sometimes not fully usable “designed” eye relief. We
measure and list the actual usable eye relief so that people in the real
world can pick the eyepieces that will work best for them.

A binocular or spotting scope whose body is clad in rubber or
polyurethane armor is said to be armored. Armor can be applied for
looks, a better grip, noise-proofing, etc. An armored body does not
guarantee that a binocular or spotting scope is waterproof, although
most waterproof optics are armored.

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Clear skies,
Astronomics

This Nikon 10x25mm Travelite multicoated high power compact binocular has aspherical eyepiece elements for low distortion, plus costly BaK-4 porro prisms for more performance than you might expect from its low price . . .